Geoarchaeological survey on the island of Gozo combined with test excavations and new chronometric dating of two Neolithic temple sites at Santa Verna and Ġgantija on the Xagħra plateau have revealed well-preserved buried soils which tell a new story of soil development and change for the early-mid-Holocene period. Micromorphological analysis has suggested that the earlier Neolithic climax soil type was a thick, well-developed, humic and clay-enriched argillic brown Mediterranean soil. With human intervention on the Xagħra Upper Coralline Limestone plateau from at least the early 4th millennium BCE, the trajectory of soil development quickly changed. Radical soil change was marked by the removal of scrub woodland, then consequent poorer organic status and soil thinning, and rubefication and calcification, no doubt exacerbated by Neolithic agricultural activities and a more general longer-term aridification trend. The beginnings of this transitional brown to red Mediterranean soil change process has been observed at Santa Verna temple by the early 4th millennium BCE, and appears to be much further advanced by the time of the latter use of Ġgantija temple in the early-mid-3rd millennium BCE. There is also evidence of attempts at amending these deteriorating soils during this period and into the 2nd millennium BCE, a practice which probably underpinned the viability of later Neolithic agricultural society in the Maltese Islands. The changes observed ultimately resulted in the creation of the thin, xeric, red Mediterranean soils on the Coralline Limestone mesa plateaux which are typical of much of Gozo and Malta today.

Previous studies have suggested that excess variations from single-photon counting systems used in luminescence dating may result in underestimation of errors and profoundly influence age models. In this study ten different photon counting systems have been investigated to explore this effect with a greater number of photomultiplier types and instrumental architectures. It is shown that radiation induced phosphorescence from F1 feldspar produces a controllable low-level light source whose local variance approximates Poisson expectations. However excess variation in dark counts was observed to varying extents from all systems. The excess variance is slightly anti-correlated with the age of the system, with older devices conforming more closely to Poisson behaviour. This observation does not seem to fit the hypothesis that enhanced levels of helium diffused into older tubes increase non-Poisson components. It was noted that a significant part of the non-Poisson behaviour was associated with multi-event pulse streams within time series. Work was also undertaken to develop mitigation methods for data analysis and to examine the implications for dating uncertainties in a test case. A Poisson-filtering algorithm was developed to identify and remove improbable multi-event streams. Application to data from signal-limited single grains of sediments from a Neolithic chambered tomb in Corsica has shown that, for this case, removing non-Poisson components improves the robustness of retained data, but has less influence on overall dating precision or accuracy. In signal limited applications use of this algorithm to remove one source of excess variation is beneficial. The algorithm and test data are appended to facilitate this.

2017

Muñoz-Salinas, E., Castillo, M., Sanderson, D., Kinnaird, T.: Geochronology and landscape evolution of the strand-plain of the Usumacinta and Grijalva rivers, southern Mexico.Journal of South American Earth Sciences.79,394--400 (2017).

The strand-plain of the Usumacinta and Grijalva rivers is the largest of the Gulf of Mexico as it is characterized by a sequence of well-preserved beach-dune ridges (n > 100) distributed ∼150 km along the shoreline. This prominent coastal landform is part of the delta plain of Tabasco and Campeche. We present geochronological data of the beach-dune ridges sequence of the Usumacinta and Grijalva rivers. Radiocarbon dating failed in providing consistent ages of the ridges in contrast to optically stimulated luminescence (OSL), which yielded coherent and robust dates. The oldest beach-dune ridges were formed ∼2.5 ka. The presence of blocked-valley lakes evidences a recent process of sediment aggradation on the delta plain caused by a marine transgression. Using a regression model with the OSL ages and the distance of beach-dune ridges from the shoreline we estimate that the autoretreat yielded the sediment accumulation ∼7 ka. Our estimation agrees with other general models of sea level rising in the Gulf of Mexico that consider a marine stabilization initiated about ∼6–7 ka. The progradation rates of the beach-dune ridges (4.7–8.9 m yr−1) place this strand-plain among those with high sedimentation rates in the Gulf of Mexico and, perhaps, around the world.

A high-resolution chronostratigraphy has been established for an eroding Atlantic round house at Sloc Sàbhaidh (North Uist, Scotland), combining detailed OSL profiling and dating of sediments encompassing the main bracketing events associated with the monument, radiocarbon AMS dates on bone recovered from excavated features and fills within it, and TL dates on pottery and burnt clay. Concordant OSL and radiocarbon evidence place construction of the wheelhouse in the first to second centuries AD, contemporary with dates from the primary occupation. Beneath the wheelhouse, clay deposits containing burnt material, attest to cultural activity in vicinity to the monument in the preceding second to first centuries BC. At a later date, the southern wall collapsed, was rebuilt, and the interior spaces to the monument re-structured. The chronology for the later horizons identified from the sediment luminescence dates extends to the second half of the first millennium AD, which goes beyond the range of the radiocarbon dates obtained. The data from ceramics encompass both periods. The juxtaposition of the dating evidence is discussed relative to short and longer chronologies for this Iron Age monument. Corollaries of this research are the implications that based on the long chronology, some of the ecofacts (bone) appear to be residual, and that the temporal duration of Hebridean Coarse Ware may extend into the second half of the first millennium AD.

Turner, S., Bolòs, J., Kinnaird, T.: Changes and continuities in a Mediterranean landscape: a new interdisciplinary approach to understanding historic character in western Catalonia.Landscape Research.1-17 (2017).

To understand why historic landscapes changed in the past researchers need to identify when and where changes took place, but in rural landscapes, the origins and development of many historic elements including field systems, roads, terraces and other earthworks remain poorly understood. This paper outlines a practical interdisciplinary method using GIS-based historic landscape characterisation (HLC) to integrate data from different sources and model how historic character varies in space. It pilots an innovative approach using luminescence profiling and dating that can underpin the HLC with significantly improved knowledge of historic processes of change. We focus on four case studies of terraced agricultural landscapes in western Catalonia and demonstrate for the first time that existing terrace systems often have medieval or early modern origins.

Abstract Dating agricultural terraces is a notoriously difficult problem for archaeologists. The frequent occurrence of residual material in terrace soils and the potential for post-depositional disturbance mean that conventional artefactual and lab-based dating methods often provide unreliable dates. In this paper we present a new technique using luminescence field profiling coupled with OSL dating to produce complete (relative) sequences of dates for sedimentary stratigraphies associated with agricultural terraces and earthworks. The method is demonstrated through a series of case-studies in western Catalonia, Spain, in which we reconstruct the formation sequence of earthwork features from the Middle Ages through to the present day. OSL profiling at the time of archaeological survey and excavation permitted spatially and temporally resolved sediment ‘chronologies’ to be generated, and provides the means to interpret the environmental and cultural archives contained in each. The case-studies presented here show that luminescence approaches are a valuable tool to reconstruct landscape histories.

The Kyrenia Range underwent tectonically driven uplift during the Pliocene to Pleistocene in response to the interaction of various tectonic processes.To understand the tectonic processes driving the uplift and how this is related to uplift of other areas of the Eastern Mediterranean, uranium-series disequilibrium and optically stimulated luminescence dating were applied to marine and non-marine terrace depositsexposed on the northern flankof the range. Palaeomagnetism and strontium isotope dating were used in conjunction to date the final stages of the marine environment adjacent to the Kyrenia Range prior to major surface uplift.Uplift rates range from >1.2 mm a−1, inferred during the Early Pleistocene, to <0.2 mm a−1 during the Late Pleistocene. The new data show that the Kyrenia Range was uplifted contemporaneously with the Troodos Massif in southern Cyprus.The uplift of the Kyrenia Range appears to have been significantly faster than that affecting other comparable regions in the easternmost Mediterranean during the Pleistocene (e.g. Lebanon coast; southern Anatolian plateau). The driving mechanism for the uplift of both the Kyrenia Range and the Troodos Massif is inferred to be the collision of the Eratosthenes Seamount with the Cyprus trench to the south of Cyprus.

Muñoz-Salinas, E., Castillo, M., Sanderson, D., Kinnaird, T., Cruz-Zaragoza, E.: Using three different approaches of OSL for the study of young fluvial sediments at the coastal plain of the Usumacinta–Grijalva River Basin, Southern Mexico.Earth Surface Processes and Landforms.41,823-834 (2016).

We use three different approaches of optically stimulated luminescence (OSL) to study young fluvial sediments located at the main channels of one of the largest fluvial systems of North America: the Usumacinta–Grijalva. We use the Pulsed Photo-Stimulated Luminescence (PPSL) system also known as portable OSL reader, full OSL dating and profiling OSL dating in samples extracted from vertical sediment profiles (n = 9) of riverbanks to detect changes in depositional rates of sediments and to obtain the age of the deposits. The results of the PPSL system show that the luminescence signals of vertical sediment profiles highly scattered from the top to the bottom contrast with the luminescence pattern observed on well–reset sequences of fluvial deposits where luminescence increase from the top to the bottom of the profile. The profiling and full OSL ages yielded large uncertainty values on their ages. Based on the inconsistencies observed in both ages and luminescence patterns of profiles we suggest that these fluvial deposits were not fully reset during their transport. As an explanation, we propose that in the Usumacinta and Grijalva rivers the cyclonic storms during the wet season promote the entrainment of large volumes of sediments due to high-erosional episodes around the basin resulting from hyper-concentrated and turbid flows. We conclude that the PPSL, profiling and full OSL dating of sediments are useful tools to quantify and to assess the depositional patterns in fluvial settings during the Holocene. These techniques also can yield information about sites where increases in the sediment load of rivers may produce poorly resetting of grains affecting the results of OSL dating.

2015

Abstract Young sediments, with low sensitivity and low dose rates, are challenging for luminescence dating. Here, we present work on the site of Sandwick South, a Norse settlement, in which these challenges were present. Field gamma dose rates below 0.1 mGy a−1, and total dose rates of 0.4–0.5 mGy a−1, combined with expected ages of less than 1 ka, resulted in a requirement for quantitative determination of equivalent doses of 0.2–0.4 Gy. The bedrock geology of the area are metagabbros, which explain both the exceptionally low dose rates and the lack of autochthonous quartz. Luminescence profiling during fieldwork revealed stratigraphically progressive ØSL\ and \IRSL\ signals, indicating phases in the sediments with dating potential. While laboratory characterisation recovered some quartz, its low yields and luminescence sensitivity precluded application of quartz methods. Electron microscopy confirmed the presence of feldspars, which were separated and used for \IRSL\ Single Aliquot Regeneration Additive (SARA) analysis. Counting times for both high resolution gamma spectrometry (HRGS) and thick source beta counting (TSBC) measurements were extended by 1 order of magnitude, resulting in overall uncertainties of <6% for these low dose rates. Dose estimates were obtained using an adapted \SARA\ protocol, incorporating long overnight preheats before first measurement, with the aim of mitigating short-term fading effects. Using these procedures, archaeologically meaningful dates were obtained from this difficult material, which are internally consistent, coherent with stratigraphy, and concordant with the radiocarbon constraints of the associated archaeological settlement. The dates demonstrate sand accumulation in the early to mid-13th century \AD\ and also in the 18th century AD, which are contemporary with disruptive sand movements registered in other coastal regions of the Northeast Atlantic and North Sea regions. The approaches adopted here have provided solutions to the challenging conditions of this young, insensitive material and can therefore be considered to extend the range and applicability of luminescence dating methods.

Abstract This paper aims to date the construction and demise of the medieval bridge at Avignon by integrating sedimentological and stratigraphic evidence with geophysical surveys (ERT), optically stimulated luminescence (OSL) and radiocarbon chronologies. In this way the palaeo-environments of Barthelasse Island (Avignon) and the Labadie Plain (Villeneuve-les-Avignon) have been reconstructed, and the physical evidence of this iconic landscape placed in temporal and historic frameworks. In the course of this work the location of piers 9 and 10 (partly destroyed and buried today beneath sediments) of the former masonry bridge were re-discovered and cored to ca. 7 m depth. 14C dating of large fragments of wood (Abies Alba Mill.), from the pier settings, provides the first direct age determination (1213–1280 and 1238–1301 cal. AD) of the constructional phases for the stone bridge at ~ 1250 ± 30 \AD\ and reveals an allochtonous origin of the timber (fir tree) used to support it. This new date from a primary context post-dates the historical attribution based on the Benezet legend (dated to 1177–1185 cal. AD). These results suggest that the material associates with a rebuilding phase, potentially between \AD\ 1234–1237, following the destructive activities of the French Army of Louis \VIII\ during the siege of Avignon in \AD\ 1226. Additionally, the integration of sedimentological data, ØSL\ sediment dating, and 14C results reveal that major detrital phases overlie the bedrock followed by rapid accretion of ca 3 to 7 m of sand to around 1650 ± 50 AD. This relates to the later stages of the Little Ice Age which are characterised by repeated floods and high sedimentation rates in the Lower Rhone River. In this period, the sedimentary archives and chronology record evidence of major environmental change, coincident with the political and economic conditions during the reign of French King Louis \XIV\ and with the final demise of the medieval bridge across the Rhone at Avignon.

2014

Muñoz-Salinas, E., Bishop, P., Sanderson, D., Kinnaird, T.: Using OSL to assess hypotheses related to the impacts of land use change with the early nineteenth century arrival of Europeans in south-eastern Australia: an exploratory case study from Grabben Gullen Creek, New South Wales.Earth Surface Processes and Landforms.39,1576--1586 (2014).

Abstract We study the paraglacial activity in Gredos Gorge, a glaciated valley of Sierra de Gredos (Central Spain), using geomorphic markers, stratigraphy and an approach based on OSL. We use luminescence signals from debris flow and fluvial deposits as well as ØSL\ dating of three deposits to detect the main paraglacial processes in Gredos Gorge. We identify two major phases of paraglacial activity during and after the retreat of Last Glacial Maximum (LGM) glaciers. The first phase consisted of high discharge debris flows, sourced up-valley, triggered during the deglaciation. The second phase started ~ 11 ka and is characterized by two processes: (1) the triggering of low discharge debris flows sourced on the flanks of moraines, and (2) the reworking of paraglacial deposits by rivers. Our results of ØSL\ signals, stratigraphy markers and sediment volume indicate that during and after the deglaciation of Gredos Gorge, paraglacial sediment was depleted as theory predicts. However, glacigenic sediments have not been transferred to sediment sinks as long as ~ 70% of glacial deposits are still stored in the valley. The transition of the environmental conditions prevailing during the ŁGM\ to current Mediterranean climate seems to play an important role in delaying the exhaustion model of glacially-conditioned sediment release. We propose that the poor coverage of vegetation driven by the Mediterranean climate prevents the stabilization of glacigenic sediment that is only mobilized during high discharge events responding to extreme rainfalls.

Excavations at Meadowsfoot Beach, Mothecombe, south Devon, between 2004 and 2011 focused on two main areas. In the first, evidence for occupation in a sand dune included successive hearths and imported early medieval finds. In the second, three phases of early medieval structures were uncovered, along with more imported finds including amphora sherds. At least one of the structures was very large, and is presently unique in Devon. The landscape context of the site is considered along with the impact of sea-level change and coastal erosion. The paper concludes with a discussion of the site and its relationship to post-Roman networks of trade and communications with late Antique Atlantic Europe and the Mediterranean. We argue that Mothecombe helps us towards a better understanding of these networks by furnishing new insights on their social foundations in western Britain.